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Mission to chart a 3D map of the Milky Way

The second release of results from the European Space Agency's Gaia mission takes place to the world scientific community. Gaia Data Release 2 (GDR2) marks an enormous step forwards for astronomy, providing a map of the Milky Way galaxy in orders of magnitude larger and more precise than that available previously.

Gaia has been in routine operations for nearly four years. This ambitious space astronomy project aims to map a substantial part of our galaxy over a mission lifetime of more than 5 years, eventually scanning the entire sky around 70 times.

The spacecraft orbits the Earth at a distance of 1.5 million kilometers in the Lagrange-2 region, 4 times further away than the Moon. This is a quasi-stable point in the Sun-Earth system with an orbital period of one year, in the opposite direction to the Sun as seen from Earth.

Gaia scans continuously with a rotational period of 6 hours, building up a map of the sky with exquisite angular resolution, unhampered by the blurring effects of the Earth's atmosphere. GDR2 contains the positions, distances, optical brightness and colours of more than one billion stars. Supplementary information in the form of spectroscopic radial velocities, variability light curves and stellar astrophysical parameters are also available for subsets of the main catalogue. This release of data marks a major leap forward in our knowledge of the Galaxy with 500x more stellar distances measured than in the first data release in September 2016. That previous release was in itself a significant step forward, with 20x more stellar distances measured than by the precursor Hipparcos mission in the early 1990s.

A small team of scientists and developers based in the Wide Field Astronomy Unit of the Institute for Astronomy (IfA) in the School of Physics and Astronomy have been working on the project for more than ten years. The team currently comprises Michael Davidson, Nigel Hambly and Nick Rowell. The team is responsible for several key calibration subsystems within the on-ground data processing pipelines that have been developed for Gaia by a collaboration of hundreds of engineers and scientists spread around Europe. Further details of the IfA's involvement can be found in a previous School News item coinciding with the launch of Gaia back in December 2013.

Dr. Hambly reported "This is a significant milestone for the Gaia project and demonstrates the superb quality of the data gathered so far. The information content of GDR2 is a huge step forward and we are continuing to work on improvements for later data releases."

Dr. Davidson said "The launch of Gaia brought many surprises and challenges as we came to know the spacecraft. Now each data release is eagerly anticipated by the astronomy community."

Dr. Rowell commented "The Gaia catalogue represents an enormous and rich dataset that will be exploited by astronomy researchers for decades to come."

GDR2 represents only an intermediate step in the science exploitation of Gaia data, being based on 22 months of observations. The European teams within the Gaia Data Processing and Analysis Consortium are already working on the next data release with improved software and calibrations. GDR3 will take place towards the end of 2020, and will contain the analysis of around 36 months of data. The calibration improvements coupled with more measurements taken over a longer time will lead to even greater precision in the 3D positions and space motions contained within the multi-billion row Gaia star catalogue.

The Wide Field Astronomy Unit's participation in the European Space Agency Gaia Data Processing and Analysis Consortium is funded by grants from the UK Space Agency and Science and Technology Facilities Council.

Image gallery

Gaia's sky in colour (Copyright ESA/Gaia/DPAC)Gaia's all-sky view of our Milky Way Galaxy and neighbouring galaxies, based on measurements of nearly 1.7 billion stars. The map shows the total brightness and colour of stars observed by the ESA satellite in each portion of the sky between July 2014 and May 2016.

Gaia’s second data release (Copyright ESA)Based on 22 months of observations, the second release of Gaia's data contains the position on the sky and brightness of 1 692 919 135 stars, as well as measurements of the parallax and proper motion of 1 331 909 727 stars. It also includes a wide range of additional information including the colours, radial velocities, estimate of the surface temperature and radius and luminosity of numerous stars.

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